Extreme pressure lubricants containing molybdic xanthates



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United States Patent ()flice EXTREME PRESSURE LUBRICANTS CONTAINING MOLYBDIC XANTHATES' Georges Hugel, Ville dAvray, Seine-et-Oise, and Robert *C'itilitrtl, Paris, France, assignors' to Institut Frangiais'd'u Petrole des Carburants et Lubrifiants, Reuil-Malmaison, 'S eine-et-Oise, France grante- Filed an- 5 sa- N 80 6 priority, application France Jan. 7, 1954 The present invention is concerned with lubricants -cgnt ainingmolybdic xanthates and being capable of use temperature and pressure conditions. I

is known that the use of solid substances such as,

for example, graphite or molybdenum sulfide, for coatthecontact surface of metallic parts subjected to fricn faci litate s the sliding thereof, considerably reducing their coefiicient of friction and wear. Generally, this A g is realized with the aid of a solution prepared incorporating-into a lubricant (oil or grease) .a coll oi dal suspension of graphite or of molybdenum sulfide. I Yhese thereupon form a deposit which fills the irregularities in the surfaces and protects them, even if the lubricant should. happen not to reach any diflicultly accessible ofthe contact surfaces. However, such asolution is bound, up with the disadvantage which is inherent in every. colloidal suspension, namely, that it is subject to 11' ulation under the influence of a change in the oil,

h causes it to lose all its eflicacy.

primary object of the present invention is to remedy t hisljdeficiency. This is realized, briefly stated, by means ,pf asplution prepared by dissolving in the oil or grease a soluble compound of molybdenum which decomposes under the influence of the temperatures and pressure locally attained by friction, said solution having the property of depositing a sulfur compound of molybdenum on themetallic surfaces.

Prjeferred, among the soluble compounds of molybdenum, are the molybdic xanthates of the formula 'wherein R is an alkyl group since, according to the presentfinventionfthese decompose at the temperatures attained by friction.

"Bestfadap'tedlfor good lubrication purposes are those xanthates of the preceding formula which are derivatives the temperature at which the molybdenum compound, decomposes in the oil, e.g. from about 300 C. for the isobutyl derivative to about 170 C. for the decyl derivative.

Montequi (An. Espan. FisQuim. 1930, 28, 481) has I described'm'olybdic xanthates of the foregoing formula wherein thealkyl groups contain 2, 4 and 5 atoms, i.e.

' thefethylg is obutyl and isoamyl derivatives. (Montequi did not' envisiage the possibility of using the said xan- .as lubricant additives.) The aforesaid molybdic T x 'arithates wherein R contains from 6 to 12 carbon atoms 2,951,040 Patented Aug. 30, 1960 To obtain such a coating, the metallic part is immersed in a bath prepared by dissolving molybdic xanthate (preferably a derivative of a higher alcohol) in mineral oil, e.g. in an amount to provide a 0.5 to 10%, preferably an 8%, solution by weight, by heating the mixture to a temperature above the decomposition temperature of the molybdic xanthate (between about 170 and 380 C.) and maintaining such temperature for a period of from /2 hour to 2 hours.

Particularly good results are obtained at a temperature of about 300 to 320"v C., maintained for a period of 2 hours. The duration of the treatment period can be reduced by employing a higher temperature.

The 'value of such a preliminary coating is clearly demonstrated by the result of tests carried out with the so-called Four-Ball Machine (as described by Boerlage in Engineering, July 14, 1953, page 46). Using an oil which contains 2% by weight of molybdic decylxanthate: with a seizing delay of 2 seconds, pressures above 140 kg. could not be attained; with a seizing delay of 60 seconds, pressures above about kg. could not be attained. On the other hand, if the balls were preliminarily provided with a coating as aforedescribed, the pressure could be raised to about 310 kg. with a seizing delay of 15 seconds. This is a remarkable performance, the impression left on the ballsnot exceeding the plastic deformation due to these high pressures. There is thus practically no wear. The table which follows shows the principal results of tests carried out with an oil containing 2% by weight of molybdic decylxanthate:

Results of tests on Four-Ball Machine" It is evident from this table that the performances obtained when employing a preliminarily-applied protective coating are superior to those obtained with the aid of a lubricant alone.

However, this coating is subject to progressive elimination due to friction. To avoid such elimination, i.e. to retain the coating, it is preferred to use a lubricant containing in solution an organic compound of molybdenum which is decomposable under the influence of the pressure and temperature produced by friction. Such a lubricant thus makes it possible constantly to renew the protective coating in proportion to its wear.

Illustrative of the lubricants suitable for this purpose are inter alia the following:

An oil containing in solution an organic compound of molybdenum, soluble in the oil and decomposable under the influence of the pressure and the temperature produced by friction, and particularly a mineral oil containing either a molybdic xanthate or hydrocarbon-soluble molybdenum blue;

A solution of a nitrogenous thiornolybdate in a vegetable or animal oil or in an oil constituted by a mixture of esters of fatty acid and alcohol or by a mixture obtained from transesterification of vegetal or animal oils with polyethylene or polypropylene glycol or a higher alcohol, or by the synthetic products from the esterification of mono or polyalcohols with fatty acids or from the esterification of diacids with monoalcohols; and particularly a solution of a nitrogenous thiomolybdate in a diol, glycol, polyalcohol or polyethyleneglycol; the lubricants thus obtained having the property of decomposing at temperatures and pressures produced by friction.

Among others the following specific oils can be used as lubricants according to the invention:

Castor oil Peanut oil Olive oil OX-foot oil Fish oil v Monooleates of polyethylene glycols Monooleates of butylene glycols Monooleates of propylene glycols Monooleates of polytrimethylene glycols Palmitates of polypropylene glycols Dioleates of polyethylene glycols Dioleates of butylene glycol Dioleates of polypropylene glycols Dioleates of polytrimethylene glycols Bishexyl sebacate Bishexyl adipate Bishexy-l methyl adipate Bisheptyl sebacate Bisheptyl adipate Bisheptyl methyl adipate Bisoctyl sebacate Bisoctyl adipate Bisoctyl methyl adipate Bisnonyl sebacate Bisnonyl adipate Bisnonyl methyl adipate Bisdecyl sebacate Bisdecyl adipate Bisdecyl methyl adipate Bisundecyl sebacate Bisundecyl adipate Bisundecyl methyl adipate Bisdodecyl sebacate Bisdodecyl adipate Bisdodecyl methyl adipate Decane diol Octane diol Hexane diol Lubricants containing hydrocarbon-soluble molybdenum blue, as well as those obtained with the aid of a nitrogenous thiomolybdate, are disclosed and claimed in copending applications filed on even date herewith by Georges Hugel for Hydrocarbon-Soluble Molybdenum Blues, Serial No. 480,612, filed January 7, 1955, now Patent No. 2,852,469 (corresponding to RV. 661,055, filed in France on January 6, 1954) and for Lubricants Containing Nitrogenous Thiomolybdates (corresponding to P.V. 661,056, filed in France on January 6, 1954).

The present invention encompasses within the scope thereof lubricants produced with the aid of molybdic xanthates, and also those'molybdic xanthates per se of the hereinbeforegiven formula wherein R contains 6 or more carbon atoms, as for example molybdic decylxanthate, molybdic dodecylxanthate and molybdic hexylxanthate.

The principal results of tests using as lubricant, by way of exampie, an oil containing 2% by weight of molybdic decylxanthate, have been set forth above. The table which follows sets forth results obtained with the 4- Ball Machine, while insuring retention of the protective coating by means of an oil containing 1% by weight of molybdenum blue:

t Tests on Four-Ball Machine 01L WITH 1% OF MOLYBDENUM BLUE This table shows that performances obtained while insuring retention of the protective coating by a lubricant with a hydrocarbon-soluble molybdenum blue base are remarkable since it is possible therewith to attain a pressure of 350 kg. with a seizing delay of 39 seconds.

It is also possible to use any one of the lubricants which come into consideration for the formation, and not only for the maintenance, of the said protective coatmg.

Comparable results are then attained provided that the increase in pressure is progressive and is effected with continuous lubrication. In fact, under the influence of the temperature attained by friction, a molybdenum sulfur compound is deposited in successive layers on metallic parts subject to friction, resulting simultaneously in the formation and in the maintenance of a protective coating.

The performances thus realized, with continuous lubrication by the progressive application of constantly increasing pressures, have already been set forth in connection with lubricants containing a nitrogenous thiomolybdate (thiomolybdate of an organic nitrogen base) in copending application, Ser. No. 480,611, filed January 7, 1955, now Patent No. 2,909,541 (corresponding to P.V. 661,056 in France). The table which follows sets forth results of tests obtained under the same conditions with a lubricant containing, for example, 2% by Weight of molybdic decylxanthate:

Tests with Four-Ball Machine [Mineral oil S.A.E. 30 (viscosity at 50 O.=54 centipoises) +2% by weight of molybdic decylxanthate (1 mm. at; each load with the some balls, with pfiog'ressively increasing pressures and without preliminary coa mg Ooefiieient cl Friction Diameter Load Applied Delay in of Impresln kg. Seizing in sion in seconds Before Maxi- After mm. Seizing mum seizing 60 0. ll 1. l.

The following examples set forth representative embodiments of preparing molybdic xanthates according to this invention (percentages are by weight and yields are molar yields):

. Example 1 U produced a white precipitate which, on contact with the air, becomes rose-colored. After incorporation of all the xanthate and stirring for a half-hour, about two liters of acetic acid (diluted in a proportion of one volume of acetic acid for four volumes of water) are introduced dropwise, while cooling constantly, until -a pH of 4 is attained. The obtained violet-red colored precipitate is then extracted with light petroleum ether.

The solution in petroleum ether, after decantation, is dried over anhydrous magnesium sulfate, filtered, and freed of petroleum ether by evaporation under reduced pressure on a water-bath. There are obtained as residue 400 grams of molybdic decylxanthate in the form of a very dark red, almost black, oily mass (which represents a yield of 70% relative to the theoretical yield). Molybdic decylxanthate corresponds to the formula:

This mass, which is very soluble in mineral oils, is preferably maintained under refrigeration until it is ready for use (by incorporation into a lubricant oil, according to the present invention).

Example 2 The process according to Example 1 is followed, except that the ammonium molybdate solution is intimately admixed with a solution in two liters of water of 2 mols (568 grams) of sodium dodecylxanthate.

The procedure being otherwise the same, there are obtained 450 grams of molybdic dodecylxanthate, which rep Twenty parts by weight of ammonium molybdate are dissolved in 100 parts by volume of water. The resultant solution is poured into 1000 parts by weight of the solution in 250 parts by weight of water of 50 parts by weight of hexylxanthate.

Then there are gradually added 25 parts by volume of an aqueous acetic acid solution of 20% strength. The resultant organomolybdic compound is then extracted with benzene, the latter is eliminated from the extract by boiling on a water-bath, first under atmospheric pressure and finally under a pressure of mm. of Hg. There are thus obtained 37 parts by weight of molybdic hexylxanthate, which corresponds to a yield of 76.4% of the theoretical. Molybdic hexylxanthate corresponds to the formula:

In the foregoing, parts by weight bear the same relation to parts by volume as do grams to milliliters.

In any of the foregoing examples the extraction of the molybdic xanthate may as well be achieved by means of a saturated paraffinic hydrocarbon having preferably less than 8 carbon atoms; such as for example pentane or isopentane, hexane-n, heptane-n, octane-n or mixtures such as petroleum ether having a boiling point of 50 to 120 C.

According to the first of the aforementioned copending applications, a hydrocarbon-soluble molybdenum blue can be prepared from a molybdenum blue which is soluble e.g. in isobutyl alcohol, by dissolving the last-mentioned blue in isobutyl alcohol to which has been added an organic liquid, such as a higher alcohol, which is simultaneously soluble in isobutyl alcohol and in hydrocarbons, then expelling the isobutyl alcohol, and finally concentrating the remainder down to a suitable concentration whereby excess solvent is eliminated. The starting molybdenum blue can also be extracted from its aqueous solution by means of a phosphorus compound, such as diethylamido-di-decylphosphate, which is soluble in oil but not in water.

According to the second of the aforementioned copending applications, a thiomolybdate of an organic nitrogen base, as for example triethylamine, is prepared from a soluble thiomolybdate and a soluble salt, e.g. the hydrochloride of the base, whereby the desired organic base thiomolybdate is precipitated. These thiomolybdates are soluble in lubricant bases, including polyalcohols and the like, and are thermally decomposable to yield sulfur compounds of molybdenum for coating parts which are subject to friction.

Having thus disclosed the invention, what is claimed is:

1. A lubricant consisting essentially of a mixture of about to 99.5% by weight of a lubricating mineral oil and about 0.5 to 10% by weight of a molybdic xanthate having the formula wherein R stands for an alkyl radical with 6 to 12 carbon atoms.

2. A lubricant according to claim 1 wherein the molybdic xanthate is molybdic decylxanthate.

3. A lubricant according to claim 1 consisting essentially of about 98% by weight of the mineral oil and about 2% by weight of the molybdic xanthate.

4. A lubricant according to claim 1 wherein the molybdic xanthate is molybdic dodecylxanthate.

5. A lubricant according to claim 1 wherein the molybdic xanthate is molybdic hexylxanthate.

6. A lubricant according to claim l consisting essentially of about 92% by weight of the mineral oil and about 8% by weight of the molybdic xanthate.

References Cited in the file of this patent UNITED STATES PATENTS 1,740,809 Cronshaw et a1. Dec. 24, 1929 2,173,383 Carter Sept. 19, 1939 2,346,155 Denison et al. Apr. 11, 1944 2,363,884 McCleary et al. Nov. 28, 1944 2,394,954 Watkins Feb. 12, 1946 2,436,051 Mixon Feb. 17, 1948 2,758,089 Hoif et a1. Aug. 7, 1956 

1. A LUBRICANT CONSISTING ESSENTIALLY OF A MIXTURE OF ABOUT 90 TO 99.5% BY WEIGHT OF A LUBRICATING MINERAL OIL AND ABOUT 0.5 TO 10% BY WEIGHT OF A MOLYBDIC XANTHATE HAVING THE FORMULA 